The present invention relates to a double glazing having a plurality of sheet glasses juxtaposed in the direction of thickness with spacers arranged in between, peripheries of these sheet glasses being sealed throughout the circumference thereof.
Generally, the above double glazing is sealed at the peripheries thereof with an organic sealant, but this has been unsatisfactory in fully inhibiting gas transmission. Thus, it has been considered to seal with low melting point glass having a high sealing performance with respect to gas, instead of using the organic sealant. However, the low melting point glass used conventionally is baked at 450xc2x0 C. or higher, and ordinary sheet glass is used as the above sheet glasses.
Recently, the above double glazing has been required to have both functions of high strength glass and thermal insulation performance where it is desired to use the double glazing as window panes of multistory buildings or glass for vehicles in which a high degree of wind pressure resistance is required, or as window panes or the like required to have fire retardant property.
However, the conventional double glazing noted above has a problem that its strength could be insufficient.
Having regard to the above problem, the present invention has for an object to provide a double glazing having high strength and thermal insulation performance.
A double glazing according to the present invention has the following characterizing features:
The double glazing according to claim 1 is characterized in that reinforced sheet glass is employed for at least one of a plurality of sheet glasses, the peripheries of said sheet glasses being sealed by a sealing material having a sealing temperature below 400xc2x0 C.
Wind pressure strength and fire retardant property are improved by employing reinforced sheet glass for at least one of said plurality of sheet glasses.
In this case, conventional low melting point glass used for sealing double glazing must be baked at 450xc2x0 C. or above to provide sealing, and therefore the surface compression stress retained on the surfaces of the sheet glass by a reinforcing process could be lost in time of the baking, thereby failing to demonstrate high strength.
However, since, in the present invention, sealing is provided by a sealing material having a sealing temperature below 400xc2x0 C., the sheet glasses may be bonded together without losing the surface compression stress of the reinforced sheet glasses, thus maintaining the strength.
FIG. 1 shows a relationship between retention time and residual strength under different retention temperatures of a reinforced soda lime glass of 4.6 mm in thickness. That is, FIG. 1 is a view showing how stress is eased with the passage of time where the reinforced soda lime glass is retained at predetermined fixed temperatures. The retention temperatures are set at every 50xc2x0 C. between 200xc2x0 C. and 600xc2x0 C.
The results show that residual strength after retention at 450xc2x0 C. for 30 minutes lowers to about 25%, but only to about 65% after retention at 400xc2x0 C. for 30 minutes. That is, to improve residual strength, the lower sealing temperature is the better. It will be seen that a sealing temperature below 400xc2x0 C. results in a seal little affecting the strength of the sheet glass.
FIG. 2 shows an example of reinforced soda lime glass of 9.5 mm in thickness. This case also shows a tendency similar that in FIG. 1, and no difference due to the thickness of the sheet glass is seen.
In the double glazing according to claim 2, said sealing material may comprises low melting point glass having a bonding strength of at least 20 kg/cm2 and a coefficient of thermal expansion at 75-85xc3x9710xe2x88x927/xc2x0C.
By using the low melting point glass having the above bonding strength, this glass adheres tight to the sheet glasses to maintain an excellent seal over a long period of time.
Moreover, the coefficient of thermal expansion of this low melting point glass is 75-85xc3x9710xe2x88x927/xc2x0C. which is smaller by 5-15xc3x9710xe2x88x927/xc2x0C. than the coefficient of thermal expansion, 85-90xc3x9710xe2x88x927/xc2x0C., of ordinary sheet glass. As a result, the bonding strength is maintained without impairing the seal against a compressive force acting on a fused portion to crack the fused portion.
In the double glazing according to claim 3, said low melting point glass may comprise glass powder of a composition including 70.0-80.0% by weight of PbO, 5.0-12.0% by weight of B2O3, 2.0-10.0% by weight of ZnO, 0.5-3.0% by weight of SiO2, 0-2.0% by weight of Al2O3, 3.0-7.0% by weight of Bi2O3, 0.5-5.0% by weight of CuO, and 0.1-6.0% by weight of F(F2).
Where the low melting point glass of this composition is used, fluidity is high and residual stress may be reduced even at a temperature of 400xc2x0 C. or below.
With this composition in particular, the above characteristic is outstanding where the mole ratio of Cu+/(Cu++Cu2+) in the low melting point glass is 50% or more.
The coefficient of thermal expansion of the low melting point glass may be matched to the coefficient of thermal expansion of the sheet glasses by appropriately mixing the low melting point glass with ceramic powder.
In the double glazing according to claim 4, said low melting point glass may have a composition including 70.3-92.0% by weight of PbO, 1.0-10.0% by weight of B2O3, 5.2-20.0% by weight of Bi2O3, 0.01-8.0% by weight of F2, 0-15.0% by weight of ZnO, 0-5.0% by weight of V2O5, 0-2.0% by weight of SiO2, 0-2.0% by weight of Al2O3, 0-2.0% by weight of SnO2 and 0-4.0% by weight of BaO, B2O3/PbO being in a weight ratio of 0.11 or less.
Where the low melting point glass of this composition is used, excellent fluidity is maintained even at a temperature of 400xc2x0 C. or below, to seal the sheet glasses without application of a strong pressure. Thus, the double glazing may be manufactured with improved efficiency. The coefficient of thermal expansion of the low melting point glass may be matched to the coefficient of thermal expansion of the sheet glasses by appropriately mixing the low melting point glass with ceramic powder.
In the double glazing according to claim 5, said low melting point glass may have a composition including 65.0-85.0% by weight of PbO, 1.0-11.0% by weight of B2O3, 7.2-20.0% by weight of Bi2O3, 0-6.0% by weight of F(F2), 0-11.0% by weight of ZnO, 0-4.0% by weight of V2O5, 0-3.0% by weight of SiO2+Al2O3, 0-5.0% by weight of SnO2, 0-0.1% by weight of Fe2O3 and 0.2-5.0% by weight of CuO.
Where the low melting point glass of this composition is used, residual stress in time of sealing may be reduced.
As in the third and fourth characteristic compositions, the coefficient of thermal expansion of the low melting point glass may be matched to the coefficient of thermal expansion of the sheet glasses by appropriately mixing the low melting point glass with ceramic powder.
The sheet glass according to claim 6 may be float glass of a composition including 70.0-73.0% by weight of SiO2, 1.0-1.8% by weight of Al2O3, 0.08-0.14% by weight of Fe2O3, 7.0-12.0% by weight of CaO, 1.0-4.5% by weight of MgO and 13.0-15.0% by weight of R2O (R being an alkali metal), and the reinforced sheet glass may be heat reinforced sheet glass or chemically reinforced sheet glass.
Where said sheet glass is float glass having the above composition and, moreover, heat reinforced sheet glass or chemically reinforced sheet glass is used as said reinforced sheet glass, a seal is provided by baking the above low melting point glass, without significantly lowering the strength of the reinforced sheet glass, to form a sealed space between the sheet glasses.
The double glazing according to claim 7 is characterized by comprising heat reinforced sheet glass having a surface compression stress, after said sealing, in a range of 204 or more to less than 650 kg/cm2.
This reinforced sheet glass has a higher wind pressure strength than ordinary float glass. Consequently, the reinforced sheet glass may be formed thin when used for a curtain wall of an ordinary building. As a result, the reinforced sheet glass becomes lightweight, which provides an advantage of facilitating a mounting operation at an elevated location.
The double glazing according to claim 8 is characterized by comprising heat reinforced sheet glass having a surface compression stress, after said sealing, in a range of 650 or more to less than 1500 kg/cm2.
The reinforced sheet glass of this construction has a high impact resistance as noted above. Thus, where it is used for a glass door at an entrance, for example, said glass door does not break easily when a passing person should inadvertently collide with the glass door.
Even when the reinforced sheet glass should break, it would break into numerous fragments to assure an excellent safety aspect.
The double glazing according to claim 9 is characterized by comprising heat reinforced sheet glass having a surface compression stress, after said sealing, in a range of 1500 or more to 2400 kg/cm2 or less.
The reinforced sheet glass of this construction has a high surface compression stress as noted above. Thus, this reinforced sheet glass may be used as a heatproof reinforced glass for preventing spreading of fire, for example.
In the double glazing according to claim 10, said reinforced sheet glass may be a chemically reinforced sheet glass obtained by a low temperature ion exchange method in which the sheet glass is immersed in a soaking liquid heated to 350-530xc2x0 C., to exchange alkali ions in the glass with ions having a larger radius.
Also where said reinforced glass is the above chemically reinforced glass, a seal is provided by baking the above low melting point glass, without significantly lowering the strength of the reinforced sheet glass, to form a sealed space between the sheet glasses.
In the double glazing according to claim 11, said plurality of sheet glasses may define a space therebetween maintained in a decompressed state.
By maintaining the space between said plurality of sheet glasses in a decompressed state as noted above, the heat insulating property of said space may be maintained over a long period of time.
As set forth in claims 1 to 11, the sealing material having a high bonding strength and sealing performance is used to maintain the space between the plurality of sheet glasses in a highly airtight condition, thereby to demonstrate excellent insulation.
Compared with use of a conventional sealing material, a seal may be provided at a low temperature to maintain the strength of the sheet glass. Thus, the invention provides a double glazing which may be used for window panes of multistory buildings and window panes of vehicles, and for fire protection, and so on.